This invention relates to a pure galactosyltransferase isoenzyme, GT-II and to the method for its purification.
The enzymes known generically as glycosyltransterases participate in the biosynthesis of complex carbohydrates. They are commonly found as both membrane-bound enzymes within the interior of the cell and as soluble enzymes in biological fluids. The function of adding sugars to proteins is not clear, although the nature of the terminal sugar appears to be important in the control of secretion and in the clearance of circulating glycoproteins, the control of differentiation and cell-cell interaction. The biosynthesis of ABO blood group substances also requires sugar additions through the action of glycosyltransferases. Although some glycosyltransterases appear to be membrane-associated enzymes when prepared from tissue homogenates, these transferases have also been detected as soluble enzymes in various body fluids, including rat and human serum.
It has been reported in Biochemical and Biophysical Research Communications, Vol. 65, No. 2, pp. 545-551 and Proceedings of the National Academy of Sciences, U.S.A., Vol. 73, No. 4, pp. 1319-1322 that there exists two isoenzymes of serum galactosyltransferase. The isoenzyme identified as GT-II was shown to be found predominantly in patients with neoplastic disease. There is a correlation of serum GT-II levels with the extent of malignancy which apparently is independent of the site of the neoplasm. The preoperative level of GT-II activity appears to correlate with the overall extent of the tumor. Thus, the level of serum GT-II increases in association with the progression of the disease. It is not known whether the galactosyltransferase (GT-II) is merely produced by the cancerous cells or is somehow involved in the mechanism of concerous cell reproduction.
It is also shown in U.S. patent application, Ser. No. 948,252, filed Oct. 3, 1978, entitled "Method and Composition for Inhibition of Growth of Transformed Cells and Tumors", that a substrate for the galacosyltransferase isoenzyme (GT-II) also has the characteristic of inhibiting growth or destroying concerous cells and/or cancerous tumors. The inhibitor is found present in the cancerous cells or malignant tumors or in the body fluids such as sera of animals, including humans which are afflicted with cancer. The inhibitor also is found in vitro in transformed animal cells. The inhibitor is obtained by subjecting either the body fluid containing the inhibitor or the fluid obtained from malignant cells to a separation procedure which includes a step for concentrating glycoproteins from the fluid being treated and at least one chromatographic step in order to recover a fraction of glycoprotein having a molecular weight of about 3600.+-.3000.
It would be highly desirable to provide pure GT-II galactosyltransferase isoenzyme thereby to provide a means for producing and harvesting an antibody for GT-II. Such an antibody would be useful in means for assaying for GT-II if the GT-II used to form the antibody were sufficiently pure. Furthermore, such an antibody would be useful for inhibiting growth of cancerous cells and/or cancerous tumors as does the naturally-occurring inhibitor for GT-II.